Monochrome Films. During the manufacturing process, film emulsions are sensitized to various colors of the spectrum, enabling them to respond to light of all colors as well as shorter UV wavelengths. However, this response does not perfectly align with the human eye’s perception of light and dark colors. Panchromatic (pan) film, for instance, renders violet, blue, and orange-red tones somewhat lighter, while greens appear darker than typically perceived. This difference is generally accepted and beneficial, as it allows slow-pan materials to be handled under deep green darkroom-safe lighting. For a more precise match to human vision, a pale-yellow camera filter can be used.
Certain black and white films, known as orthochromatic (‘ortho’), are insensitive to the red end of the spectrum beyond approximately 590 nm. These films reproduce red as black and orange as very dark on the final print. Ortho materials, primarily sheet film, are advantageous for copying black and white prints or drawings without involving colors and can be conveniently handled in the darkroom under red safelight illumination. They are also utilized in various medical, forensic, and scientific photography applications. When subjects are illuminated by tungsten light, which contains a higher proportion of red wavelengths, the speed rating of ortho film is lower compared to daylight or flash.
Additionally, there are very slow films designed for printing darkroom rather than camera use, with sensitivity only to blue (and UV) light. These films are used to produce copy negatives, typically in large formats for special printing processes. Specialized films for camera use, in conjunction with ‘black’ filters, can be made to respond only to infrared and UV light, effectively ignoring the visible spectrum.
Color films, both negative and slide types, consist of a stack of six or more emulsion layers with three kinds of color sensitization. The top layer is sensitive solely to blue, while subsequent layers respond to blue and green, and the remaining layers primarily to red. A yellow filter is often incorporated below the blue-sensitive layer to prevent blue light from penetrating further into the film. Consequently, the multi-layered emulsion responds individually to blue, green, and red – the three primary sections of the spectrum. Each of these emulsion types eventually forms its image in a different colored dye to reproduce the final image in full color.
The relative sensitivity of the various layers, known as the color balance of the film, is meticulously controlled during manufacturing. Most color films are balanced for accurate color reproduction under daylight or flash illumination (5000–6000 K). Additionally, there are tungsten-balanced films available, which have slightly slower red-sensitive layers to ensure correct reproduction of subjects lit by the red-rich 3200 K tungsten lamps. Beyond ‘daylight’ and ‘tungsten’ balanced films, there are exceptional materials sensitized to infrared or specialized laboratory light sources.
